Point inter_point(Point A,Point B,Point C,Point D)///返回直线AB和线段CD的交点
{
    if(!intersect(A,B,C,D)) return {-INF*1.0,0};///判断直线AB是否与线段CD相交，不相交必须须特判
    double area1=fabs((B-A)*(C-A));
    double area2=fabs((B-A)*(D-A));
    double x=(area1*D.x+area2*C.x)/(area1+area2);
    double y=(area1*D.y+area2*C.y)/(area1+area2);
    return {x,y};
}

bool intersect(Point A,Point B,Point C,Point D)///判断直线AB是否与线段CD相交
{
    if(((C-A)*(B-A))*((D-A)*(B-A))<eps) return true;
    return false;
}